An abdominal aortic aneurism is a dilatation of a vessel on the abdominal aorta. This condition is treated by insertion of a so-called stent graft, i.e. composite angioplasty devices. Guide wires and catheters are inserted into the aorta via both groins and one or more stent grafts are introduced via said guide wires and catheters. An abdominal aortic aneurism A of this type is shown by way of example in FIG. 1a. It is treated by insertion of a stent graft S. Guide wires and/or catheters K are inserted into the aorta via both groins and the stent grafts are introduced with the aid of said guide wires and catheters.
The aim when inserting said stent grafts is to place the “landing zone” of the vascular graft as far as possible in the healthy vessel wall region, though at the same time taking care that no important branch vessels are covered. In particular the branches of the renal arteries, of the superior mesenteric artery (arteria mesenterica superior), of the truncus coeliacus, and of the internal iliac arteries (a. iliaca interna) must be kept free. A sensitive point is the placement of the “main stent” in the aorta, in which case the cited branch vessels must not be occluded. In the case of complex stents which include the leg arteries, as shown for example in FIG. 1c, the final stent must sometimes be composed of “partial stents” (e.g. an aortic stent (I) to which the stent for the leg artery (II) is attached through what is termed a fenestration).
In order to avoid the necessity of injecting contrast agent to allow constant vessel visualization for monitoring purposes during the complex stent positioning procedure it is possible to overlay a reference image (anatomically correctly) in the manner of a positioning aid, which reference image renders the vessels (in this case aorta and branch vessels). As shown in FIG. 2a, said reference image can either be a 2D angiogram (DSA) or, as shown in FIG. 2b, it can beneficially be a previously recorded 3D dataset (e.g. a CT angiography sequence) of the aneurysm. These show more details and can be overlaid at any angulation of the C-arm.
As shown in FIG. 3, it is possible to pre-segment the aneurysm from the reference images. In this case the course of the vessel (centerline) or the contours of the vessels can be determined, for example. This can happen both in the case of the 2D reference image, as shown in FIG. 3a, and in the case of the 3D reference image, as shown in FIG. 3b. Furthermore it is possible to identify and track instruments (e.g. catheters or guidance devices) in 2D images. As already shown in FIG. 2, a partially flexible 2D-3D or 3D-3D registration, e.g. of 2D and 3D angiography images, is possible.
A problem with said overlays is that the reference image (2D or 3D) shows the vessel anatomy at a specific instant in time. If, as shown e.g. in FIG. 4, the physician introduces very inflexible or rigid instruments, e.g. a catheter K, the anatomy is deformed. If said deformation is not corrected in the overlaid reference image (see FIGS. 4a and 4b), an imprecision or a discrepancy arises when the reference image is superimposed. This can lead to uncertainties in navigation during an intervention in which the overlay serves as a navigation aid.